A stepping motor is also called a pulse motor, a stepping motor, a stepper motor, or a digital motor, and is a motor that is driven by a pulse and functions as an actuator for digital control devices. Compact electronic apparatuses suitable for portable applications have been developed and miniature and light-weight stepping motors find widespread use as an actuator for these electronic apparatuses. Typical of these electronic apparatuses are timing devices such as an electronic watch, a timing switch and a chronograph.
In a stepping motor 10 for use in such a timing device as shown in FIG. 11, a disklike rotor 13 with two magnetic poles is sequentially rotated within a unitary stator 12 delineated with magnetically saturated sections 17 with their outer edge notched, and the rotor 13 is rotated by a drive pulse of an appropriate frequency, for example, 1 Hz, and the rotary force of the rotor 13 drives watch hands. To avoid faulty driving of the watch hands, checking that the rotor 13 rotates normally by the drive pulse is important, and for this reason, a current or a voltage feedback-induced in a driving coil by the rotation of the rotor 13 is thus detected as shown in FIG. 12.
As shown, a first peak PM1 opposite in polarity to a drive pulse PW appears as a current (feedback-induced current) feedback-induced by the rotation of the rotor 13 when the rotor 13 passes a position 90 degrees spaced from a stable position. The rotor 13 rotates further, and when the rotor 13 passes a stable position B in the opposite polarity side, which is a destination (in the opposite polarity), 180 degrees apart, past a position A where the feedback-induced current becomes zero, a large first peak PP1 having the same polarity as the drive pulse PW appears. Second peaks PM2 and PP2 are generated along with swings (vibration) until the rotor 13 is stabilized and stops.
Although the first peaks PM1 and PP1 are strong in level, they are affected by transient currents TW of the drive pulse PW, and it is difficult to separate the first peaks PM1 and PP1 from the drive pulse PW in time. In the conventional watch hand driving, the second peaks PM2 and PP2, though they are weak in strength but easy to separate, are chopper-amplified by a chopper pulse, and are captured as a feedback-induced current, and used to detect the rotation of the rotor.
Today, a variety of functions are incorporated in a timing device such as a wristwatch, and in one of such functions, a stepping motor is driven faster than normal hand driving to set time automatically or manually. A quick-moving operation under which the stepping motor is driven fast requires that the drive pulse be supplied at a short period. For time setting, the watch needs to be driven paying attention not to cause faulty watch hand driving, namely, not to cause an erratic rotation of a rotor.
It is an object of the present invention to provide an electronic apparatus that allows a stepping motor to perform reliably a quick-moving operation.